This invention relates in general to the pumping of fluids and deals more specifically with a down hole pump which has particular utility in pumping highly viscous oil and oil that is heavily gaseous.
Conventional down hole pumps used in oil wells operate by alternately creating suction and pressure in a pumping chamber that is submerged in the oil column in the well. Vacuum is created in the pumping chamber in order to draw in fluid when the pump is open, and the fluid is subjected to pressure in the pumping chamber when the pump is closed. The pressure causes the fluid to be pumped to the surface. Proper performance of this type of pump requires that the pumping chamber be sealed at all times, and this is not always possible, especially if the components of the pump have been subjected to extensive service. Any components of the pump that have been worn to the point of leaking cause the pump to malfunction.
Conventional pumps which rely upon suction are unable to effectively pump highly viscous oil. When viscous oil is to be pumped, the suction in the pump chamber is often insufficient to draw the oil into the pump. Due to the high viscosity of "heavy oil", it does not respond to vacuum in the same manner as lighter oil, and the vacuum is unable to draw the highly viscous oil into the loading chamber in sufficient quantity for the pump to operate effectively. As a consequence, pumps which operate on the basis of vacuum are unable to function at all or at best are only marginally effective in pumping highly viscous oil. Screw pumps must therefore be used to pump heavy oil, and they are less than satisfactory in a number of important respects.
Conventional pumps are also subject to "gas locking" which makes them ineffective in pumping gaseous oil. If gas laden oil is encountered, the gas is sucked into the pumping barrel along with the oil, thus inhibiting the pumping action. When a considerable volume of gas is present in the pumping chamber, the gas is compressed and expanded during pumping strokes and the pump energy is expended in gas compression rather than in pumping of liquid. Once a sufficient quantity of gas is present to create what is known as "gas locking" in the industry, the pump is unable to develop a vacuum in the loading chamber and additional fluid is not drawn into the pump. At this point, liquid is either not pumped at all or at best is pumped in only minimal quantities. The "gas locking" problem is particularly severe in stripper wells where enhanced recovery methods such as gas injection are often used, and much effort and financial resources have been devoted to its solution without significant success.